I'm no expert and I'm sure many of my designs are flawed. My understanding and application has come from over a decade of doing ,reading ,trying ,.....etc. My understanding of all this is that increasing pipe diameter increases flow rates while decreasing velocity. Higher velocities result in higher friction losses. One of the things I've read and heard ,over and over, is that you want to avoid restricting the intake side of a pump and I've heard this from people that employee pumps in other areas and fields as opposed to just the aquarium sector. One thing that can happen with high intake velocities is cavitation. My advice was offered based on using the same pump in similar applications. Like I said before there are always going to be compromises. If you want to really figure it all out , I'll refer you to this
article .
A quote from the above referenced article:
Quote:
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One problem is thinking that if the pump you are using has a ¾” or 1” inlet or outlet that is the size of plumbing that should be used.
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I'm not saying that 1 1/2" on the inlet is going to be a problem, I'm saying that I would have used 2" to decrease velocity and resistance. You're right in that Lowe's doesn't carry 2" flex PVC, you have to go someplace else for that (pool and or plumbing suppliers.)
One can obviously over think and over engineer anything to the point of diminishing returns.